1. Field of the Invention
The invention relates to unidirectional fluid valves, especially the exhalation valve of a respirator face mask and, to a lesser extent, the inhalation valve.
2. Description of the Related Art
A typical respirator face mask such as that shown in U.S. Pat. No. 4,414,973 (Matheson et al.) has an air-purifying filter extending from each cheek area, between which is mounted an exhalation valve directly in front of the wearer's mouth and nose. Increasing the sizes of the air-purifying filters increases the filtering efficiency, or functional life, and lowers the breathing resistance, but may require a reduction in the size of the exhalation valve if the exhalation valve is kept in the same position and out of the wearer's field of vision. Any reduction in the size of the exhalation valve increases the pressure drop through the exhalation valve, making it more difficult for the wearer to breathe.
The exhalation valve of FIG. 9 of the Matheson patent has an annular seat at the periphery of an annular orifice that can be closed by a flap 450 which "is molded with a conical configuration, with the interior concavity seating against the edge 416 of the seat 410" (col. 9, lines 13-15). The flap flexes in the direction of the arrows B to the dotted position when the user exhales.
Siebe North Inc. respirator face piece No. 7700 has an exhalation valve similar to that of the Matheson patent except that its flap is nearly flat (slightly concave toward the seat) and has been formed with diametrically aligned ribs so that upon being lifted off the seat, it assumes substantially the shape of a portion of a cylindrical surface. By doing so, the flap should exert less resistance to being lifted from the seal ridge valve seat than when its entire circular periphery is lifted to the same extent.
Inhalation valves of respiratory face masks are usually constructed in the same manner as are the exhalation valves. The inhalation valve of FIG. 10 of the Matheson patent shows a disk-like flap 338 being moved in the direction of arrows A to the dotted shape during inhalation. In FIG. 13, the same flap 338 is said to be "oriented in a concave manner (viewed from the outlet) so as to move more readily from its seating surface. This avoids the popping associated with prior art valves" (col. 8, lines 26-29). Inhalation valves, however, are not required to seal as effectively on closure as are exhalation valves, and in some respiratory face masks do not maintain full contact between the flap and seat in the rest position.
In the respirator face mask of FIG. 4 of U.S. Pat. No. 4,630,604 (Montesi), the flap of the exhalation valve 26 appears to have the same shape at rest as does that of the inhalation valve of FIG. 13 of the Matheson patent.
3. Other Related Art
Of possible pertinence to the present invention are prior disclosures of valves which would not be useful as exhalation valves for respirator face masks, but have uses to which unidirectional valves of the present invention could be put. One of these, U.S. Pat. No. 771,327 (Schmidt), concerns a valve which is especially adapted for use in pumps working with a high vacuum and mentions steam-turbines, gas-compressors, and vacuum pumps. It shows in FIGS. 1 and 2 a valve having a seat 8 in the form of a portion of a cylindrical surface and formed with passages 9 that can be closed by a spring 12 of the same form. The spring, which may be rectangular or may have the shape shown in FIG. 2, is attached to the center of the seat, and its free ends lift to the position shown in FIG. 1 to allow fluid to pass upwardly through the passages 9.